 We examined the use of the Green-Red Vegetation Index, GRVI, as a phenological indicator for multiple ecosystems in Japan. Our findings suggest that GRVI equals 0 can be used as a reliable threshold for detecting the early stages of leaf growth and the middle phases of autumn coloring. Additionally, we observed that GRVI can provide a clear distinction between different ecosystem types and respond to subtle disturbances. This article is authored by Takashi Motoka, Kenlo Nishida Nasahara, Satoshi Sachida, and others.